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It is possible to implement AES on 4-bit microcontroller? As far as I know, AES on 8-bit microcontroller are common especially for light weight application such as the RFID.

I have yet to come across AES been employed on 4-bit microcontroller, therefore I have been wondering whether such implementation is feasible.

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Using two 4 bit data structures you can construct an 8 bit data structure. So in that manner it is definitely possible to put AES on a 4-bit microcontroller. –  mikeazo Feb 3 '12 at 15:53
    
can you elaborate more? –  cLaRe Feb 3 '12 at 15:58
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it would be similar to multiple precision integer arithmetic (see cacr.math.uwaterloo.ca/hac/about/chap14.pdf for details). –  mikeazo Feb 3 '12 at 21:26

2 Answers 2

Yes, AES could be implemented on a 4-bit micro-controller such as this EM6626, and that would not be rocket science or stupidly slow. This application note illustrates that all kind of 8-bit operations are simple, and table lookups are possible.

In fact, tables are not even indispensable if performance is non-critical; see this minimalist AES source code in C which has a compilation option to avoid any table.

The most serious issue is the amount of RAM required: current 128-bit subkey and 128-bit data will eat half of the total 512-bit RAM of the above device.

Also worrying is the security: I know no 4-bit micro-controller with any kind of security evaluation. Thus I would trust such an implementation only if it is operated in a secure environment, and with a key that vanishes from the device after use. That's an appropriate security model for an enciphering machine, but not a copy-protection dongle.

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thanks for the information. by any chance that AES in the field of GF((2^4)^2) would be efficient for 4-bit MCU in comparison to the AES in the field of GF((2^2)^4) and GF(((2^2)^2)^2)? –  cLaRe Feb 6 '12 at 13:21

The paper Enabling Standardized Cryptography on Ultra-Constrained 4-bit Microcontrollers (page 255) describes such an implementation.

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That's a good reading there... With a practical approach.. –  uygar.raf Feb 17 '12 at 21:52

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